Komuniecki P R, Kochan R G, Schlender K K, Reimann E M
Mol Cell Biochem. 1982 Oct 29;48(3):129-34. doi: 10.1007/BF00421224.
Glycogen synthase in skeletal muscle of 3-day alloxan-diabetic rats was found to be in a less active state than in normal muscle. Both the activity ratio (activity without G6P divided by activity with 7.2 mM G6P at 4.4 mM UDPG, pH 7.8) and fractional velocity (activity with 0.25 mM G6P divided by activity with 10 mM G6P at 0.03 mM UDPG, pH 6.9) were significantly lower in the diabetic tissue. Correspondingly, the S0.5 for UDPG and A0.5 for G6P were significantly higher in diabetic tissue, suggesting decreased affinity for substrate and activator, respectively. The kinetic changes in the diabetic synthase were identical whether the alloxan-treated animals were maintained on insulin for 7 days prior to withdrawal for 3 days, or studied 3 days immediately after alloxan treatment. The diabetes-induced changes in synthase could be reversed by injecting the diabetic rat with insulin 10 min prior to sacrifice. After insulin treatment, the S0.5 for UDPG and A0.5 for G6P decreased to control levels or lower and the activity ratios and fractional velocities increased to control levels or higher. The activity of glycogen synthase phosphatase was not decreased in diabetic skeletal muscle. This observation, coupled with the rapid response of the diabetic synthase to in vivo insulin treatment, suggests that, unlike the phosphatase in cardiac muscle and liver, the glycogen synthase phosphatase in skeletal muscle is not altered by the diabetic state.
研究发现，3天龄四氧嘧啶糖尿病大鼠骨骼肌中的糖原合酶活性低于正常肌肉。糖尿病组织中的活性比（在pH 7.8、4.4 mM UDPG条件下，无G6P时的活性除以有7.2 mM G6P时的活性）和比速度（在pH 6.9、0.03 mM UDPG条件下，有0.25 mM G6P时的活性除以有10 mM G6P时的活性）均显著降低。相应地，糖尿病组织中UDPG的S0.5和G6P的A0.5显著升高，分别表明对底物和激活剂的亲和力降低。无论四氧嘧啶处理的动物在停药前接受7天胰岛素治疗后停药3天，还是在四氧嘧啶治疗后立即研究3天，糖尿病合酶的动力学变化都是相同的。在处死前10分钟给糖尿病大鼠注射胰岛素，可以逆转糖尿病诱导的合酶变化。胰岛素治疗后，UDPG的S0.5和G6P的A0.5降至对照水平或更低，活性比和比速度升至对照水平或更高。糖尿病骨骼肌中糖原合酶磷酸酶的活性并未降低。这一观察结果，再加上糖尿病合酶对体内胰岛素治疗的快速反应，表明与心肌和肝脏中的磷酸酶不同，骨骼肌中的糖原合酶磷酸酶不会因糖尿病状态而改变。
